Introduction 3 



concentrating coil to ponder on the problem on and off for 15 

 years, and well he deserved to be the discoverer of electron 

 optics ! 



When these discoveries had opened the way, the idea of an 

 electron microscope emerged in many minds.* Work was started 

 almost at once in two places — by Knoll and Ruska at the Tech- 

 nische Hochschule, Berlin, and by Briiche and his collaborators 

 in the A. E.G. laboratory. f The first results, still very modest, 

 comparable perhaps with the resolution of a good magnifying 

 glass, were published in 1932. In another 4 years, the electron 

 microscope had just about reached the resolving power of the 

 ordinary microscope, and in 4 more years it had overtaken and 

 beaten it by a factor of about a hundred. At this limit something 

 like a brick wall was reached. 



The greater half of this monograph will be devoted to a survey 

 of the development which led the electron microscope to the 

 present limit of about 8A, where it has come to a stop. Toward 

 the end, suggestions will be discussed by means of which the 

 brick wall may perhaps be breached. Finally it will be shown 

 that after overcoming this obstacle, there will be another, at about 

 0.5A, made of much more impenetrable material than bricks. 

 There is no detail in Nature finer than about 0.5A, which could 

 be resolved by any microscope, however perfect. In other words, 

 resolution will have to stop here for lack of objects. But the 

 interval between 0.5 A and 8A probably contains objects of 

 sufficient interest to make such an effort worth while. 



* The author remembers discussions on the possibiHty of an electron 

 microscope in Berlin physicist circles as far back as 1927. 

 t Allgemeine Elektrizitatsgesellschaft, Berlin. 



^^\CAl 



